The present invention refers to an improved disposable syringe.
As is known, a syringe generally comprises a cylindrical body open at the rear to receive a plunger. An internally hollow needle is mounted at the head of the syringe body. The liquid contained in a vial is drawn into the syringe body through the needle by retracting the plunger. The liquid contained in the syringe body is injected into the patient""s body through the needle by pressing on the plunger.
Because of health regulations and to avoid transmission of infectious diseases, syringes must generally be used only once and then discarded. For this reason there is a growing demand on the market for disposable syringes able to prevent re-use.
Moreover, syringes generally have drawbacks from a safety viewpoint. In fact, once the syringe has been used, the needle remains exposed at the head of the syringe body, with the risk of injury and accidental stabs.
This drawback is overcome in part by European patent EP 0636381 which describes a guard device for syringe needles. In this case, when the plunger of the syringe reaches the end of its stroke, the front end of the plunger stem captures the needle. Once the injection is completed, the user must manually retract the stem; in this manner the needle is pulled inside the syringe body by the head of the stem into the safety position which prevents accidental stabs.
This solution presents the drawback that the user, having finished the injection, can forget to carry out retraction of the stem, leaving the needle exposed and thus rendering the protection device ineffective.
Patent application PCT WO 99/37345 by the same applicant as the present application describes a disposable safety syringe which has a needle-covering sleeve mounted axially on the syringe body and slidable from a retracted position, in which it leaves the needle exposed to allow injection, to an advanced position in which it completely covers the needle, preventing re-use of the syringe and acting as a guard against accidental stabs.
Once the injection has been carried out, the sleeve is automatically brought into the extracted safety position, by means of an automatic mechanism and without any intervention by the user. Nevertheless, this solution has a certain complexity due to the provision and movement of the needle-covering sleeve.
The object of the present invention is to eliminate the drawbacks of the prior art providing an improved disposable syringe that is practical, versatile, economical and simple to make.
Another object of the present invention is to provide such a disposable syringe which is able to prevent further attempts at use.
Another object of the present invention is to provide such a disposable syringe that is extremely safe and able to prevent accidental wounds after use thereof.
These objects are achieved according to the invention with the characterstics listed in appended independent claim 1.
Advantageous embodiments of the invention are apparent from the dependent claims.
The disposable syringe according to the invention comprises a syringe body hollow on the inside and open at the front and rear, a plunger slidable inside the syringe body with an injection stroke extending from a withdrawn or retracted syringe-filling position to an advanced syringe-emptying position, and an injection needle integral with a needle-carrier that can be engaged to the front end of the syringe body or the plunger. The plunger is provided at the rear with a manually drivable stem driven out of the syringe body through the rear end thereof.
The peculiarity of the disposable syringe according to the invention is represented by the fact that, associated with said syringe body, retaining means are provided to retain spring means under compression and, integrally with said stem, engagement means are provided to cooperate with said retaining means to free said spring means when said plunger reaches the end of the injection stroke. In this manner, when the plunger reaches the end of the injection stroke, the spring means are automatically released from the retaining means and act on an abutment surface of the stem causing retraction thereof into the retracted position.
An advantageous embodiment of the invention for safety purposes, provides for the use of a needle-carrier mounted on the inside of the fore end of the syringe body and a stem which has a fore end with means able to couple with the rear end of the needle-carrier in order to retain it. In this manner, when the spring means cause retraction of the stem, the needle-carrier draws the needle with it into the syringe body chamber.
A further advantageous embodiment of the invention for safety purposes provides for use of a needle-carrier mounted integrally with the plunger. In this case the head of the syringe body provides sealing means to prevent leakage of the liquid from the annular gap formed between the outer surface of the needle and the inner surface of the cylindrical body. Moreover, at least one channel that puts the inner bore of the needle in contact with the chamber of the cylindrical body will be provided in the needle-carrier or in the plunger.
The advantages of the disposable syringe according to the invention are obvious. In fact said syringe, by causing automatic retraction of the stem of the plunger, once the injection is completed, prevents re-use thereof. Moreover, in the case of the needle-carrier being engageable with the plunger, re-entry of the plunger at the same time draws the needle into the chamber of the syringe body, avoiding accidental stabs with the utmost safety.